In recent years a number of new physical phenomena such as those of high temperature superconducting, giant magnetic resistance, high intensity fluorescence and catalysis have been discovered. Exploring a material and composition that develops such a physical phenomenon is carried out with a combinatorial film forming apparatus in order to reduce the time expended for material investigation. Using a combinatorial film forming apparatus allows forming a library of a group of materials possible of that developing on one substrate in one vacuum process and finding a new material and a new composition from the library or deriving a theoretical prediction from a specific character of the library. It is said that the use of a combinatorial film forming apparatus can shorten the time period of a hundred years thus far spent to a month, for a material exploration.
A combinatorial film forming apparatus makes it essential to include a means for limiting supply of materials electively to a desired portion on a substrate, a film forming means for depositing films of different kind and a structural analysis means for analyzing the structure of films of desired portion on the substrate. For example, an apparatus which uses a ablation laser for film deposition, is equipped with a plurality of masking units, a target switching unit, an ablation laser light lead-in unit, a substrate heating laser unit and a reflection high-energy electron diffraction (RHEED) unit.
And, in late years demands to find new materials of binary and ternary systems have been rising. For instance, a fluorescent material for a plasma display, which is required to possess properties different from those of a conventional electron-beam excited fluorescent material, is predicted to be realized by a new material of binary or ternary system.
Materials of binary and ternary systems have so far been investigated using a combinatorial film forming arrangements as shown in FIG. 22. FIG. 22 shows diagrammatically methods of investigating materials of binary and ternary systems with the conventional combinatorial deposition arrangements. As shown in FIG. 22(a), there are prepared a first mask 1 having a number of unmasking apertures for defining a plurality of independent specimens on a substrate, to wit to form pixels on the substrate and a second mask 2 in the form of a masking shield for selectively covering the unmasking apertures to select the pixels to be formed by vapor deposition. The relative position among the substrate, the first mask 1 and second mask 2 is adjusted to select the pixels to be formed, while a material forming the pixel by vapor deposition is selected, and this step is repeated so as to form on the substrate thin films that are of a binary or ternary phase-diagrammatic system which has predetermined ratios of components varied from pixel to pixel. Then, the pixels made are measured as to their specified properties to find out a pixel having particular properties as desired and then to determine from its ratio of components an optimum ratio of components that is required to achieve specific properties as desired.
As shown in FIG. 22(b), there is also used a rotary disk having a plurality of masks thereon, each of which are arranged to select pixels to be formed by vapor deposition, and this rotary disk is successively rotated while a material forming pixels is selected to form pixels on a substrate, which have predetermined ratios of components differing from pixel to pixel to form binary or ternary phase-diagrammatic system. Then, the pixels made are measured as to their specified properties to find out a pixel having particular properties as desired and then to determine from its ratio of components an optimum ratio of components that is required to achieve specific properties as desired.
By the way, there is a material, such as a fluorescent material, which exhibits useful properties only in an extremely narrow rage of its ratio of components. Such a case requires the conventional methods to form an extremely large number of pixels with finely varied ratios of components. In the prior method shown in FIG. 22(a), as the method requires the precise positioning among the substrate, the first mask 1 and second mask 2, however, this in turn requires spending considerable time, and in addition, as a result of which if an extremely large number of pixels are to be formed, then the film depositing conditions tend to change between the first and the last formed pixels. Thus, for example, the substrate temperature distribution and atmospheric composition could change uncontrollably with the lapse of time, giving rise to the problem that reproducible data, or reliable data can no longer be obtained.
And, while in the prior method shown in FIG. 22(b) rotation makes it sufficient to position a given mask in less time-consuming, there the limitation in volume of the vacuum unit limits the number of masks that can be mounted and it is thus difficult to form an extremely large number of pixels with finely varied ratios of components. For this reason, where an extremely large number of pixels with finely varied ratios of components must be formed, the prior art must have relied on a technique as mentioned below as regards a binary system.
FIG. 23 diagrammatically shows a conventional method of making a thin film that is binary phase diagrammatic. As shown at (a) of the Figure, there are used a first mask 1 disposed perpendicular to a flow of vapor of material A or B and having an opening, a second mask 2 in the form of a masking shield movable in a scanning manner parallel to the first mask 1 and a substrate disposed across the opening of the first mask 1. In operation, as shown in (b) the mask 2 is moved in the direction of x while material A is being vaporized. Since moving the mask 2 at a constant speed in the direction of x causes material A vapor-deposited on a region of the substrate to become thicker in proportion to the time in which it is exposed to the flow of vapor of material A, there is obtained a thickness distribution of material A that increases at a given gradient in the direction of movement, namely in the direction of x. Thereafter, if as shown at (c) the material for vapor deposition is replaced with material B and the mask 2 is moved in a scanning manner from the position opposite to that shown in FIG. 23(b) and in the direction of −x, there is then obtained a thickness distribution of material B that increases at a given gradient in the direction of movement, namely in the direction of −x. As shown at the right hand side of (c), there is thus obtained a combined thickness distribution of materials A and B made up of a film of material A whose thickness varies continuously from 0 to 100% and a film of material B whose thickness varies continuously from 100 to 0% in the direction of x. The materials A and B vapor-deposited are each extremely thin in film thickness and when coming into contact with each other are immediately mixed together into a stable state of binary material that is determined by the substrate temperature. Repeating the vapor deposition of A followed by the vapor deposition of B allows forming a thin film that is binary phase diagrammatic of a desired thickness.
This method permits obtaining a binary phase diagramming thin film in which its ratio of components continuously varies or is varied finely in the direction of x and also obtaining reliable data since the thin film can be made in an extremely short period of time. This method in a sense can be said to be a method of forming by uniaxial movement of a single mask having an opening relative to a substrate. Further, it can be said to be a method of forming by uniaxial movement of one side of the opening in the mask, namely uniaxial movement of a edge of the mask relative to the substrate. It will be apparent that this method can be expanded to form a ternary phase diagramming thin film by moving a mask edge triaxially or along three axes mutually intersecting at an angle of 120 degrees.
It is extremely difficult, however, to include such a triaxially operating masking mechanism that must necessarily become considerably large in volume in an apparatus of this type used for material exploration, e.g., in a combinatorial film forming apparatus that makes it essential to be equipped with an ablation laser light lead-in unit, a target switching unit, a substrate heating laser unit and a reflection high-energy electron diffraction unit in a vacuum chamber. This can be done, of course, by making the vacuum chamber in volume to an extent necessary to accommodate them, but so enlarging it requires augmenting the capacity of its vacuum pumping system correspondingly, thus making the apparatus highly costly.